This relates generally to integrated circuits and more particularly, to integrated circuits such as programmable integrated circuits with memory elements.
Integrated circuits often include memory. For example, random-access memory can be used to store data during processing operations. In programmable integrated circuits, random-access memory is sometimes used to store configuration data. In this context, the random-access memory is often referred as configuration random-access memory (CRAM). The outputs of CRAM cells on a programmable integrated circuit are applied to pass transistors in programmable logic circuits. The data that is loaded into the CRAM cells configures the programmable logic circuits to perform custom logic functions by turning on and off appropriate pass transistors.
To ensure that pass transistors can be fully turned on and therefore operate at high speeds, some programmable integrated circuits power CRAM cells at elevated voltages. The resulting elevated control signals that are supplied at the outputs of the CRAM cells can be used to overdrive their associated pass transistors and thereby ensure that the pass transistors are fully on.
This type of scheme generally requires that the transistors that make up the CRAM cells be fabricated with thickened gate oxides relative to the pass transistors and other logic transistors. The thickened gate oxides ensure that the CRAM transistors will operate reliably, but may involve undesired process complexity.